The Collaborative International Dictionary of English v.0.48:

Catapult \Cat"a*pult\, n. [L. catapulta, Gr. ?, prob. from kata`
   down + ? to shake, hurl.]
   [1913 Webster]
   1. (Mil. Antiq.) An engine somewhat resembling a massive
      crossbow, used by the ancient Greeks and Romans for
      throwing stones, arrows, spears, etc.
      [1913 Webster]

   2. A forked stick with elastic band for throwing small
      stones, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

catapult
    n 1: a plaything consisting of a Y-shaped stick with elastic
         between the arms; used to propel small stones [syn:
         slingshot, sling, catapult]
    2: a device that launches aircraft from a warship [syn:
       catapult, launcher]
    3: an engine that provided medieval artillery used during
       sieges; a heavy war engine for hurling large stones and other
       missiles [syn: catapult, arbalest, arbalist,
       ballista, bricole, mangonel, onager, trebuchet,
       trebucket]
    v 1: shoot forth or launch, as if from a catapult; "the enemy
         catapulted rocks towards the fort"
    2: hurl as if with a sling [syn: sling, catapult]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "catapult":
   arbalest, ballista, booster rocket, bowl, cast, chuck, chunk, dart,
   dash, fire, fling, flip, fork, ground loop, heave, hopoff, hurl,
   hurtle, jerk, lance, launch, let fly, lob, pass, peg, pelt, pitch,
   pitchfork, put, put the shot, rotation, serve, shy, sling,
   slingshot, snap, takeoff, throw, throw stick, throwing-stick, tilt,
   toss, trebuchet, wommera